GAZANIA SPP - A NEW HOST OF LETTUCE MOSAIC POTYVIRUS, AND A POTENTIALINOCULUM SOURCE FOR RECENT LETTUCE MOSAIC OUTBREAKS IN THE SALINAS VALLEY OF CALIFORNIA

Lettuce mosaic potyvirus (LMV) outbreaks in the Salinas Valley of Cali fornia have increased in recent years despite a comprehensive lettuce mosaic management program. In a previous study, it was established tha t new serologically and/or genetically distinct LMV strains were not r esponsible for these outbreaks. Therefore, the role of alternate hosts was investigated. Here we provide evidence that the ornamental plant, Gazania spp., is an alternate host of LMV. A number of lines of evide nce were used to establish that gazanias were infected by LMV, includi ng indirect enzyme-linked immunosorbent assay, dot blot hybridization with an LMV coat protein (CP) probe, and sap- and aphid-transmission o f LMV from gazania to lettuce and Nicotiana benthamiana. Additionally an LMV CP fragment was amplified from an infected gazania plant by rev erse transcription-polymerase chain reaction, and the nucleotide seque nce of this fragment was 99% identical to the CP sequence of an LMV is olate from the Salinas Valley. We further show that LMV-infected gazan ias are widely distributed in the Salinas Valley, and are present near areas where LMV outbreaks have occurred. Field experiments demonstrat ed that LMV could be transmitted from infected gazania to lettuce. LMV -infected gazanias also were found in local nurseries, suggesting that infection of gazania with LMV had occurred prior to planting in the S alinas Valley (i.e., lettuce was not serving as the source of inoculum for infection of gazania in the Salinas Valley). These results establ ish that gazania is an alternate host of LMV, and suggest that gazania s may be a primary inoculum source for recent lettuce mosaic outbreaks in the Salinas Valley.